1. Field of the Invention
The present invention relates to a vibrating gyroscope detecting system, and more particularly to a vibrating gyroscope detecting system for detecting a rotational angular velocity based on two detecting signals obtained from a vibrating gyroscope which comprises a prism-shaped vibrator.
2. Description of the Prior Art
FIG. 10 is an illustrative view showing a vibrating gyroscope in which a conventional vibrating gyroscope detecting system is used. A vibrating gyroscope 1 comprises a vibrator 2. The vibrator 2 comprises a regular triangular prism-shaped vibrating body 3, and piezoelectric elements 4a, 4b, and 4c formed at the center portion of each of three side faces of the vibrating body 3. A variable resistor 5 is connected between the piezoelectric elements 4a and 4b. An oscillation circuit 6 is connected between the variable resistor 5 and the piezoelectric element 4c. An output signal of the oscillation circuit 6 is supplied to the piezoelectric elements 4a and 4b. An output signal of the piezoelectric element 4c is fed back to the oscillation circuit 6. In the vibrating body 3, bending vibration occurs in a direction perpendicular to the surface on which the piezoelectric element 4c is formed.
The piezoelectric elements 4a and 4b are connected with a differential circuit 7. An output signal of the differential circuit 7 is detected by a synchronous detection circuit 8 and then smoothed by a smoothing circuit 9. When a rotational angular velocity is not applied to the vibrating gyroscope, the vibrating body 3 bends and vibrates in a direction perpendicular to the face on which the piezoelectric element 4c is formed, thus output signals of the piezoelectric elements 4a and 4b are the same signal. Since the rotational angular velocity is not applied to the vibrating gyroscope 1 at this time, the output signals of the piezoelectric elements 4a and 4b are driving signals. However, actually, the output signals of the piezoelectric elements 4a and 4b are different from each other due to the variation of processing accuracy of the vibrating body 3 or the piezoelectric elements 4a, 4b and 4c. Thus, the variable resistor 5 is adjusted so that the same signals are supplied to the differential circuit 7. Therefore, the output signal of the differential circuit 7 is zero.
The bending vibration direction of the vibrating body 3 is changed by a Coriolis force when the vibrator 2 is rotated on the axis of the vibrating body 3. As a result, the different signals are generated in the piezoelectric elements 4a and 4b. Since the change of the signals generated in the piezoelectric elements 4a and 4b correspond to the change in the vibration direction of the vibrating body 3, the signals generated in the piezoelectric elements 4a and 4b correspond to the rotational angular velocity. As shown in FIGS. 11(A) and 11(B), phase difference between the signal corresponding to the rotational angular velocity and the driving signal is 90.degree.. Since the driving signal components supplied from the piezoelectric elements 4a and 4b to the differential circuit 7 have the same phase and level, they are offset by the differential circuit 7. Since the piezoelectric elements 4a and 4b are positioned symmetrically with respect to the direction of the vibration of the vibrating body 3 when the vibrator 2 is not rotated, signals of opposite polarities are generated in the piezoelectric elements 4a and 4b when the vibration direction of the vibrating body 3 is changed due to the rotational angular velocity. Thus, a large signal corresponding to the rotational angular velocity can be obtained by taking the difference between the output signals of the piezoelectric elements 4a and 4b in the differential circuit 7. The rotational angular velocity applied to the vibrator 2 can be detected by synchronously detecting a positive portion or a negative portion of the output signal of the differential circuit 7 and smoothing it.
In such a vibrating gyroscope, the variable resistor is adjusted in such a manner that the output signal of the differential circuit is zero when the vibrator is not rotated. However, there is a case that the characteristics of the vibrator is fluctuated due to the change in atmospheric temperature or the like. In particular, the levels of driving signal components are fluctuated due to the change in the atmospheric temperature. When the levels of the driving signal components obtained from two piezoelectric elements are different from each other, they are not offset by the differential circuit but appears as an output signal thereof. That is, as shown in FIG. 12, the output signal of the differential circuit fluctuates due to the change in the atmospheric temperature, even though the rotational angular velocity is not applied to the vibrator. Since the fluctuation of the output signal forms a curve with the change in the atmospheric temperature, it is difficult to compensate the fluctuation. Accordingly, the driving signal component is overlapped with the signal corresponding to the rotational angular velocity, and hence it is impossible to detect the rotational angular velocity accurately.